Conventional elevator telescopic two-speed doors use two panels, two tracks, four rollers and four counter-rollers. In the case of a four panel two-speed center opening door, the situation is the same but with double elements.
Now then, this system of two tracks for the sliding of doors has various inconveniences among which the following can be cited:
Accuracy of positioning of both tracks; PA0 Special fastening to the frame of each track; PA0 Higher cost than one single track system; PA0 The tracks normally require special machining and welding and special fasteners; PA0 The rollers and counter-rollers are mounted over hanging supporting shafts with poor stiffness due to space and cost constraints; PA0 Perpendicularity and positioning are very difficult and adjustments are always needed; and PA0 These systems lead to jerking and produce distortion on rollers and counter-rollers shafts' perpendicularity.
Though there are a large number of conventional solutions, most existing telescopic doors use two parallel tracks or at best a single profile extruded with two parallel tracks in the same piece.
In any case the unit is very complex, heavy and voluminous, creating problems of misalignment and requiring unstable adjustments and, in general terms, extremely weak connections between the overhanging roller shafts and the hanging support bracket of the door.
Each one of these factors contributes to producing jerks and noise during movement of the door panels, finally giving rise to deterioration of the rollers and even the tracks
On the other hand, the door lintel on which the tracks have to be fastened must have flat support points to form exact reference points for the tracks, at least in three points. It is necessary to use separators to fasten and install the two tracks in their position.
In the same way, the rolling parts are not protected against dust and their assembly is very difficult, requiring in general terms an adjustment by means of the eccentric shafts of the upthrust rollers.
All of the above leads to problems of quality, to the need to make adjustments and to over dimensioning, causing a very high cost of manufacturing and obtainment of the system.